The induction of cyclooxygenase-2 in IL-1β-treated endothelial cells is inhibited by prostaglandin E2 through cAMP

PROSTAGLANDINS (PGs) have numerous cardiovascular and inflammatory effects. Cyclooxygenase (COX), which exists as COX-1 and COX-2 isoforms, is the first enzyme in the pathway in which arachidonic acid is converted to PGs. Prostaglandin E-2 (PGE(2)) exerts a variety of biological activities for the maintenance of local homeostasis in the body. Elucidation of PGE(2) involvement in the signalling molecules such as COX could lead to potential therapeutic interventions. Here, we have investigated the effects of PGE, on the induction of COX-2 in human umbilical vein endothelial cells (HUVEC) treated with interleukin-1 beta (IL-1 beta 1 ng/ml). COX activity was measured by the production of 6-keto-PGF(1 alpha), PGE(2), PGF(2 alpha) and thromboxane B-2 (TXB2) in the presence of exogenous arachidonic acids (10 mu M for 10 min) using enzyme immunoassay (EIA). COX-1 and COX-2 protein was measured by immunoblotting using specific antibody. Untreated HUVEC contained only COX-1 protein while IL-1 beta treated HUVEC contained COX-1 and COX-2 protein. PGE(2) (3 mu M for 24 h) did not affect on COX activity and protein in untreated HUVEC. Interestingly, PGE(2) (3 mu M for 24 h) can inhibit COX-2 protein, but not COX-1 protein, expressed in HUVEC treated with IL-1 beta. This inhibition was reversed by coincubation with forskolin. (100 mu M). The increased COX activity in HUVEC treated with IL-1 beta was also inhibited by PGE(2) (0.03, 0.3 and 3 mu M for 24 h) in a dose-dependent manner. Similarly, forskolin (10, 50 or 100 mu M) can also reverse the inhibition of PGE(2) on increased COX activity in IL-1 beta treated HUVEC. The results suggested that (i) PGE(2) can initiate negative feedback regulation in the induction of COX-2 elicited by IL-1 beta in endothelial cells, (i) the inhibition of PGE(2) on COX-2 protein and activity in IG-1 beta treated HUVEC is mediated by cAMP and (iii) the therapeutic use of PGE(2) in the condition which COX-2 has been involved may have different roles.